This invention relates in general to subsea wellheads and in particular to a load shoulder for a casing hanger that is remotely installable in a subsea wellhead housing.
When drilling a well for oil or gas, typically a wellhead housing will be mounted at the upper end of the well to a large diameter string of conductor pipe. The well is then drilled deeper and a string of casing will be run. Subsequently, the well will be drilled to a greater depth and at least one more strings of casing will be installed.
A casing hanger is located at the upper end of each string of casing, the casing hanger landing on a load shoulder in the wellhead housing. In one type of wellhead housing, the lowest shoulder is machined into the bore of the wellhead housing. Upper casing hangers are supported on lower casing hangers. In another type, the load shoulder is a separate high strength ring that is installed into a groove in the wellhead housing while the wellhead housing is being manufactured. In both cases, the inner diameter of the wellhead housing bore will decrease in a downward direction, with the smaller inner diameter located below the load shoulder.
The stepped diameter bore has a disadvantage. Drilling tools can be no larger than the minimum inner diameter located below the load shoulder. Sometimes, it is desired to utilize a drill bit or tool that is larger than minimum inner diameter.
For example, in a wellhead system that is used in containment of offshore shallow flow zones, it is desired to run a casing, which is typically 18" in diameter, through a subsea high pressure housing having a minimum bore that is typically 18.63". The nominal seat of the high pressure housing, i.e., the insert load shoulder, must be removed or left off of the assembly prior to running a high pressure housing and then reinstalled subsequent to the installation of the casing. Therefore, it is desirable to provide a means to install a nominal seat in a high pressure housing, run in an appropriate wear bushing and test the blowout preventer in a single trip, thereby saving two additional trips and the costs associated therewith.